The five co-principal investigators participating in this program have set out both collectively and individually to study the biology of lymphoid cells. Specifically, we hoped to use the techniques of cell biology and somatic cell genetics to obtain cells which have undergone mutations in one or another of the immunologically important functions which they normally perform. Wherever possible, we will use cloned cell lines in continuous culture. Mutant cells will be studied by biochemical and genetic techniques and mutant molecules will be analyzed by chemical techniques. It is hoped that a detailed study of such variants will provide a deeper insight into the structure and function of surface antigens, the production of mediators of cellular immunity, the uptake and processing of antigen, and the synthesis, assembly, secretion, function and genetic control of immunoglobulins.